The present invention is directed to an illumination unit for an apparatus, particularly for applications in the field of medicine, for example for the implementation of diaphanoscopic examinations at a human, animal or botanical examination subject, sensor applications, automotive, printing and display technology.
Description of the Prior Art
Co-pending U.S. application Ser. No. 09/359,004 discloses an apparatus for the implementation of diaphanoscopic examinations employing an illumination unit formed as a monolithic semiconductor laser diode array with separately driveable laser diodes that emit radiation. This array is followed by an optical means in the form of a micro-lens array for influencing the emitted laser beam. The separately driveable laser diodes of this apparatus make it possible to diaphanoscopically examine a specific region of a specific region, for example a knuckle gap, in limited fashion.
German PS 44 18 477, corresponding to U.S. Pat. No. 5,902,997, discloses an optoelectronic assembly with a base part on which an opto-electronic component having a number of driveable laser diodes is fixed, a lens of a lens body being respectively allocated to these diodes. The array is provided with connectors at the carrier side for driving the semiconductor array of diodes.
U.S. Pat. No. 5,327,443 discloses a semiconductor laser device with a semiconductor laser chip that is arranged on a carrier plate, wherein the semiconductor laser chip is surrounded by a frame placed onto the carrier, with a deflection mirror being disposed at the frame via which the emitted laser beam is deflected by approximately 90xc2x0. The deflected beam passes through a transparent window that is secured at the frame and covers the laser chip.
German OS 43 07 570, corresponding to U.S. Pat. No. 5,689,521 discloses a semiconductor laser light source unit wherein a rod lens or a cylinder lens for enlarging the divergence angle of the laser beam output by the semiconductor laser is arranged in front of a semiconductor laser in order to generate an essentially circular far field. By appropriate alignment of the laser chip emitting a single laser beam, a laser beam is emitted having an elliptical cross-sectional profile. The cross-sectional profile of the laser beam is circular after passing through the rod lens. A cylinder lens into which a laser beam with elliptical cross-sectional profile enters has the equivalent effect.
PCT Application WO 91/02392 also discloses an integrated micro-system with a laser system together with following optics, wherein the system is arranged on a substrate. An integrated cooling element for cooling the system is also provided.
U.S. Pat. No. 4,803,689 discloses a semiconductor laser module wherein a Peltier element is provided for temperature control.
Further, European Application 0 660 467, discloses an opto-electronic component wherein the laser chip is arranged on a common carrier between two carrier parts whose lateral surfaces neighboring the resonator faces of the laser chip are provided with mirrored layers and are inclined by 45xc2x0 relative to the resonator faces, so that the mirrored radiation emerges perpendicularly upwardly. The radiation coupled out in this way impinges a lens coupling optics into which it enters nearly perpendicularly.
A laser diode array with a diode laser bar, an electrode and a substrate that are secured to a heat sink form a diode laser unit, as disclosed in U.S. Pat. No. 5,764,675. This diode laser unit is secured to an electrical insulator plate that is in turn arranged at a heat exchanger for the elimination of heat.
Further, German OS 196 05 726 discloses an arrangement for optical coupling of a monitor diode to a laser diode, with both diodes being arranged in succession on a carrier lamella of silicon, separated by a groove. A spherical lens is arranged in the groove for coupling, which collects emitted back light and focuses it at a deflection surface where the light is reflected into the active zone of the monitor diode.
U.S. Pat. No. 5,446,750 discloses a solid state laser module with a laser diode, a solid state laser crystal and a resonator. An electronic cooling arrangement having a cooling surface at which the optical module is arranged is also provided.
A semiconductor laser device with a semiconductor laser chip and a cylinder lens for focusing the laser radiation emitted by the semiconductor laser chip is also disclosed in German OS 197 06 276. The semiconductor laser chip is secured to a base carrier part, and the cylinder lens is arranged lying on the base carrier in front of a beam exit face of the semiconductor laser chip.
German OS 197 06 279 discloses a laser device wherein a body emitting laser radiation and at least one element for beam guidance or for beam imaging are arranged in a common housing. Silicone is employed for fastening the beam guidance or imaging element.
German OS 44 10 888 discloses an arrangement for the transirradiation of human tissue, i.e. a diaphanoscopy arrangement, whereby the tissue is transirradiated with radiation having at least two different wavelengths in a radiation range of 600-1100 nm, and the minimum spacing between the wavelengths amounts to 150 nm. The tissue-specific scattered light generated in the transirradiation is subsequently detected with an image pickup system.
An object of the present invention is to provide a compactly structured illumination unit that can be versatilely employed, particularly for a diaphanoscopy device.
This object is achieved in accordance with the present invention in an illumination unit having a monolithic semiconductor laser diode bar with separately driveable drivable laser diodes that emit radiation, as well as at least one optical arrangement for collimating and/or focusing the emitted laser beam, the laser diode bar and the optical means being arranged at a common carrier, and wherein the laser diode bar is connected to a pin-like terminal elements at the carrier for diode drive, the pin-like terminal elements being in turn connectable or connected to a terminal arrangement provided at a carrier plate that accepts the carrier, and having a radiation-transparent covering that encapsulates the carrier.
In the inventive illumination unit, all required elements are arranged on a single carrier and are encapsulated with a radiation-transparent covering, so that the individual elements are protected against external influences such as dust, being touched, and the like. The carrier itself, which can inventively be a ceramic carrier, is in turn connectable or connected via pin-like terminal elements, which project laterally therefrom and via which the laser diode array is contacted at the p-side and n-side to a further carrier plate and the terminal arrangement provided thereon. In an embodiment, the carrier can be put in place as a prefabricated component part on a carrier plate of the device, or of the device control, which, for example, can be a printed circuit board. In addition, there is the possibility to connect the carrier to the ceramic carrier plate of a chip housing, i.e. the overall illumination unit can be realized in the form of an illumination chip that is in turn secured on a printed circuit board of the control unit. Overall, the inventive illumination unit represents a small-format, simply mounted and compact unit that, in particular, is well-protected due to the encapsulation.
In order to allow the possibility of a horizontal installation of the illumination unit into the device housing so that this can be kept thin and small overall, in an embodiment the optical arrangement inventively has at least one deflection mirror for deflecting the emitted laser beam. As a result, it is possible to arrange the respective components of the illumination unit, or the carrier itself, in horizontal alignment relative to the apparatus; the vertical outfeed of the laser beam being realized with the deflection mirror. A deflection by 90xc2x0 is thereby advantageous. The deflection mirror itself should be composed of a ceramic part with a vapor-deposited mirror face.
The laser diode bar or the individual diodes themselves are connected to the pin-like terminal elements with bond wires. Each laser diode thus can be directly connected to a pin-like terminal elements via a bond wire for forming a p-contact. Further, the side of the carrier that accepts the laser diode array can be at least partly covered with an electrically conductive layer, particularly a gold layer, to which the laser diode bar placed on the layer is electrically connected, and that is connected to at least one pin-like terminal means via a bond wire for forming an n-contact for the laser diode bar. As a result, the required p-contacts as well as the at least one n-contact that are required for the separate drive can be produced in a simple way.
In order to be able to implement the illumination units in as stable a fashion as possible, it has proven expedient to provide a laterally closed recess at the carrier in which the laser diode bar and the optical means are arranged, with the radiation-transparent covering being a plate or disk that closes the recess. A recess closed on all sides is provided for the acceptance of the relevant elements at the carrier, which is preferably a multi-layer ceramic carrier, this recess, of course, being deep enough so that the elements can be completely accepted therein. The ceramic carrier offers adequate protection on all sides and is sufficiently stable; the recess itself is then merely closed with the plate-like covering, so that a complete encapsulation is established with a simple design of the carrier as well as the covering.
It has proven especially advantageous for fabrication-related reasons when the optical arrangement is a pre-fabricated component part. The optical arrangement is placed completely on the carrier, which offers a considerable simplification in the assembly. The optical arrangement can be pre-fabricated as a module in this embodiment of the invention, with micro-lens systems for collimation and/or focusing as well as, if used, the deflection mirror, are arranged, for example, on a small, common carrier. The individual elements of the optical arrangement, of course, are matched to the employed laser diode bar, i.e. the succession of micro-lenses of the respective focusing systems and their number as well as the length of the deflection mirror are adapted to the spacing and number of individual laser diodes of the bar as well as to the overall length of the array, the optical arrangement also can be matched to the emitted radiation, etc. This embodiment allows the prefabricated component part to be specifically designed for a laser diode bar, such as a modular system for each laser diode bar employed.
It has proven expedient for the optical arrangement to be fashioned for collimating the emitted laser beam in two axes residing perpendicularly to one another, that in turn reside perpendicular to the beam direction, so as to generate a beam having a generally circular cross-section. This can be realized with two or more successively connected micro-lens arrays and, if necessary, micro-prism arrays that collimate the laser beam in the respectively desired axis. Such lens or prism arrays can be obtained, for example, from LIMO-Lissotschenko Mikrooptik GmbH, Dortmund, Germany.
It has proven advantageous for securing the individual elements to the carrier to secure the laser diode bar and the optical arrangement and possibly the covering as well, to the carrier with a glued connection, preferably upon using a temperature-resistant adhesive. A conductive adhesive is expediently employed for gluing the laser diode bar since the electrical contacting to the gold coating is realized thereby. The covering itself should be composed of glass, particularly anti-reflection coated glass. The laser diode bar can alternatively be secured with a solder connection.
When the laser diode bar is operated with low power  less than 15 mW, the heat that thereby arises is unproblematic and can be eliminated via the carrier. Given higher laser powers in the range between 15 mW-100 mW, this is not always possible, for which reason an arrangement for cooling the carrier is provided at the carrier, particularly in the region of the laser diode bar, in order to avoid an overheating, and thus a premature aging, of the laser diode bar. This cooling arrangement is preferably a Peltier element. This is connected via contact pins to a regulator, so that the cooling capacity can be regulated as needed.
The carrier itself is implemented as a surface mounted device that is secured or can be secured to the carrier plate in a soldering process, preferably a re-flow process.
The invention is also directed to a device for the implementation of diaphanoscopic examinations having an illumination unit of the above-described type.
Further, the illumination unit of the invention can be employed in an apparatus for printing technology, such as character printing technology, particularly written characters and image printing technology, for example offset and rotogravure technology. The inventive illumination unit also can be used in a display means, for example a display, sensor mechanism, particularly for distance-measuring technology and speed-measurement technology and/or automotive technology.